This invention relates to a coating solution for forming a colored film on a glass substrate, a glass plate (particularly automotive window glass) with such colored film, and a process for producing such glass plate.
In recent years, colored glass plates (of green, gray and other colors) have been widely used for vehicular window panes (particularly automotive side and rear windows) in order to reduce a load on air-conditioner and to suppress glare and discoloration of interior trim members. With this, it becomes possible to adequately suppress the transmission of solar radiation (i.e., infrared light, visible light and ultraviolet light) and thereby to maintain a comfortable interior environment. Furthermore, when a colored glass plate is used for an automotive window pane, it becomes possible to reduce interior visibility from outside and thereby improve privacy and to provide an ornamental effect on an automobile.
In the production of a colored glass plate by coloring a glass substrate itself, it may be necessary to add a coloring source (i.e., metal and/or metal compound) to a float glass bath when other raw materials are added thereto. This addition of coloring source is a relatively large-scale operation. Furthermore, it takes time to conduct pretreatment and post-treatment in order to replace the production of a colored glass with that of other types of glass and vice versa. Thus, the production cost of such colored glass plate is relatively high.
It is possible to easily produce a colored glass plate by forming a colored film on a transparent glass substrate with a relatively short time and a relatively low cost. It is possible to form such colored film by applying a coating solution to a surface of a glass substrate. In sol-gel process, the coating solution can be prepared by dissolving a metal alkoxide(s) and a coloring source (e.g., a metal nitrate, chloride or oxide) in a suitable solvent (e.g., alcohol). Alternatively, the coating solution can be prepared by a pigment dispersion method in which an inorganic pigment (e.g., metal oxide) or organic pigment is dispersed in a liquid. This pigment dispersion method makes the operation complicated and increases the production cost. Furthermore, a colored film prepared by using an inorganic pigment may be inferior in scratch resistance. Therefore, it may be necessary to coat such colored film with a protective film.
In sol-gel process, the coating solution is applied to a glass substrate, and then the resulting precursory film is heated into a colored film through dehydration and condensation. The resulting colored film is superior in scratch resistance. However, metal nitrate used as a coloring source in sol-gel process may generate a hazardous nitrogen oxide. The use of a noble metal or noble metal compound as a coloring source increases the production cost. The use of chromium oxide as a coloring source may induce an environmental pollution problem.
As mentioned above, it is possible to produce a colored glass plate by sol-gel process using an inorganic pigment or metal oxide as a coloring source. Even if this colored glass plate is heated at a temperature not lower than its softening point, it is impossible or difficult to completely remove color of this glass plate. Due to the existence of color, it is impossible or troublesome to recycle this glass plate in the form of cullet by putting it into a float glass bath.
It is therefore an object of the present invention to provide a coating solution which is free of the above-mentioned drawbacks.
It is another object of the present invention to provide a glass plate prepared by using such coating solution.
It is still another object of the present invention to provide a process for producing such glass plate.
It is a specific object of the present invention to provide such glass plate which is decolorized when heated at a temperature not lower than its softening point.
According to a first aspect of the present invention, there is provided a first coating solution for forming a colored film on a glass substrate. The first coating solution comprises (a) a titanium alkoxide; (b) a silicon alkoxide; (c) a coloring agent that is a nitrogen-containing organic compound; and (d) an organic solvent dissolving said titanium alkoxide, said silicon alkoxide and said nitrogen-containing organic compound.
According to the first aspect of the present invention, there is provided a first colored glass plate comprising (a) a glass substrate; and (b) a colored film formed on said glass substrate. This colored film is prepared by a process comprising applying the first coating solution to a surface of said glass substrate.
According to the first aspect of the present invention, there is provided a first process for producing the first colored glass plate. The first process comprises (a) applying the first coating solution a surface of said glass substrate, thereby forming thereon a precursory film; and (b) heating said precursory film at a temperature of 200-800xc2x0 C. into said colored film.
According to a second aspect of the present invention, there is provided a second coating solution for forming a colored film on a glass substrate. The second coating solution comprises (a) a titanium alkoxide; (b) a silicon alkoxide; (c) a nitrogen-containing organic group contained in a molecule of at least one of said titanium alkoxide and said silicon alkoxide, said nitrogen-containing organic group being derived from a nitrogen-containing organic compound; and (d) an organic solvent dissolving said titanium alkoxide and said silicon alkoxide.
According to the second aspect of the present invention, there is provided a second colored glass plate comprising (a) a glass substrate; and (b) a colored film formed on said glass substrate. This colored film is prepared by a process comprising applying the second coating solution to a surface of said glass substrate.
According to the second aspect of the present invention, there is provided a second process for producing the second colored glass plate. The second process comprises (a) applying the second coating solution to a surface of said glass substrate, thereby forming thereon a precursory film; and (b) heating said precursory film at a temperature of 200-800xc2x0 C. into said colored film.